The present invention relates generally to power converters, and, more particularly, to a switching controller circuit for a switched-mode power converter.
Switched-mode power converters transform one form of electrical energy into another, such as an alternating current (AC) into a direct current (DC) and vice-versa. Examples of switched-mode power converters include rectifiers, voltage regulators, inverters, and frequency converters. Switched-mode power converters typically include a switching controller circuit and a power converter. The power converter includes a voltage source, switches connected to the voltage source, and passive components like inductors and capacitors. The power converter is connected to an electronic component, i.e., a load, to which power is delivered.
The switching controller circuit is connected to a feedback network and receives a supply voltage of the power converter from the feedback network. The switching controller circuit controls the switches that are connected to the voltage source by outputting pulse width modulated (PWM) signals. When a PWM signal is high (i.e., logic high), the switches are turned on, and when the PWM signal is low (i.e., logic low), the switches are turned off. The switches are switched alternately on and off to control the supply voltage to the power converter. The duty cycle and time period of the supply voltage may be modified based on the voltage requirement of the power converter.
Most power conversion applications today have a digital switching controller circuit that uses a single microcontroller to control the frequency and duty cycle of the PWM signals. The power converter can operate in two modes: full-operation mode and standby mode. When the voltage requirement of the power converter is constant for a predetermined time period, the switching controller circuit operates in standby mode. In standby mode, the power converter periodically outputs voltage pulses to the switches. When the voltage requirement of the power converter varies with time, the switching controller circuit operates in full-operation mode in order to regulate the output voltage. The power converter requires high power in full-operation mode and the switching controller circuit outputs a continuous series of pulses of varying pulse widths, where the pulse width is determined by the varying voltage requirement.
The power converter requires very low power in the standby mode and hence, the switching controller circuit periodically outputs bursts of pulses, i.e., the switching controller circuit operates in a burst mode. Since the switching controller circuit comprises only one microcontroller, the cores and memories of the microcontroller operate in both the full and standby modes. This leads to large power consumption by the switching controller circuit, even in the standby mode. Other conventional switched-mode power converters include analog components, in addition to the microcontroller, to control the burst mode of operation in the standby mode, however, analog components increase cost.
A voltage-mode feedback switching controller circuit is another type of switching controller circuit that includes analog components such as a minimum duty cycle generator, a PWM generator, and a burst flip-flop. The PWM generator generates a PWM signal. When the power converter requires low power, the minimum duty cycle generator generates a PWM signal having a minimum duty cycle. When the power converter requires high power, the PWM generator generates a PWM with a varying duty cycle. The burst flip-flop controls the output of the switching controller circuit based on the PWM signal. The switching controller circuit is in standby mode when the output of the burst flip-flop is low, and in full-operation mode when the output of the burst flip-flop is high. However, the analog components such as the PWM generator, the minimum duty cycle generator, and the burst flip-flop decrease the flexibility of the voltage-mode feedback switching controller circuit by increasing the hardware dependency of the circuit.
It would be advantageous to have a low-cost switching controller circuit for a power converter that consumes less power in standby mode.